The present embodiments relate to an error protection circuit for an x-ray facility and an x-ray facility with such an error protection circuit. Error protection circuits prevent the emission of high radiation doses due to operating errors.
X-ray facilities have at least one image receiver. The image receiver records x-ray images of a patient or body to be examined, which is fluoroscopically examined by the x-ray radiation of an x-ray emitter. The image receiver has a cassette drawer in the case of cassette recording points. A cassette-type x-ray detector is inserted in the cassette drawer. The x-ray detector can, for example, be an x-ray film cassette. The cassette drawer also has an exposure measurement chamber, which is used to set automatic exposure times. The exposure measurement chamber measures the radiation dose occurring at the x-ray detector and triggers a disconnect signal for the x-ray emitter when a predetermined measurement value is reached.
Cassette drawers and other image receivers can be disposed, for example, on patient support tables, on C-arms, floor gantries or ceiling gantries. Further possibilities for the arrangement of image receivers are conceivable. Depending on which x-ray recording points are to be realized, x-ray facilities have one or more image receivers. To produce an x-ray recording, an x-ray detector has to be inserted into the respective image receiver and the x-ray emitter has to be oriented toward the image receiver.
Operator errors can occur because an x-ray detector does not have to be inserted into every image receiver and it does not have to be possible to identify from outside whether an x-ray detector is inserted. The x-ray emitter can be switched on, even though there is no x-ray detector inserted into the corresponding image receiver. The radiation dose administered to the patient is a pointless load on the examined patient or body, since no x-ray recording can be produced without an x-ray detector.
X-ray facilities with a number of image receivers require inserting the x-ray detector and activating an exposure measurement chamber assigned to the x-ray detector. It is possible that an x-ray detector is inserted into the correct image receiver but the exposure measurement chamber assigned to the x-ray detector has not been activated. Possibly an operator erroneously selects the wrong image receiver, even though they have inserted the x-ray detector into the correct image receiver. If an x-ray recording is then initiated using an automatic exposure unit, very high radiation exposure results and the erroneously selected exposure measurement chamber does not receive any x-ray radiation. The x-ray radiation strikes the exposure measurement chamber of the correct but not selected image receiver. If the selected exposure measurement chamber does not receive a radiation dose however, it also does not generate a disconnect signal for the x-ray emitter, since the dose limit value is not reached.
To avoid unnecessary radiation exposure due to such operating errors, the exposure measurement chamber signal can be observed while the x-ray recording is being produced. If after a predetermined time the measurement chamber signal is below a minimum value, incorrect operation is assumed and the x-ray recording is aborted. However, modern image receivers are so sensitive that the predetermined minimum value has to be set extremely low. The minimum value is exceeded simply by the scattered radiation occurring at the exposure measurement chamber and the x-ray recording is therefore not aborted.
In the case of x-ray facilities with a central device controller, the production of an x-ray recording is only initiated when an x-ray detector is inserted in the selected image receiver. It is only necessary to provide a detector identification, identifying the presence of an x-ray detector, in the image receiver. However, simple, manual x-ray facilities generally do not have a central controller.
DE 200 13 478 U1 discloses a solution for checking whether an x-ray detector is inserted in the image receiver and whether the grid contact of the image receiver is closed. A grid contact is used with image receivers, which have a moving scattered radiation grid. The solution disclosed in DE 200 13 478 U1 is not suitable for image receivers without or with a fixed scattered radiation grid.